Heart Rate Variability Analysis in an Experimental Model of Hemorrhagic Shock and Resuscitation in Pigs

<div><p>Background</p><p>The analysis of heart rate variability (HRV) has been shown as a promising non-invasive technique for assessing the cardiac autonomic modulation in trauma. The aim of this study was to evaluate HRV during hemorrhagic shock and fluid resuscitation, comparing to traditional hemodynamic and metabolic parameters.</p><p>Methods</p><p>Twenty anesthetized and mechanically ventilated pigs were submitted to hemorrhagic shock (60% of estimated blood volume) and evaluated for 60 minutes without fluid replacement. Surviving animals were treated with Ringer solution and evaluated for an additional period of 180 minutes. HRV metrics (time and frequency domain) as well as hemodynamic and metabolic parameters were evaluated in survivors and non-survivors animals.</p><p>Results</p><p>Seven of the 20 animals died during hemorrhage and initial fluid resuscitation. All animals presented an increase in time-domain HRV measures during haemorrhage and fluid resuscitation restored baseline values. Although not significantly, normalized low-frequency and LF/HF ratio decreased during early stages of haemorrhage, recovering baseline values later during hemorrhagic shock, and increased after fluid resuscitation. Non-surviving animals presented significantly lower mean arterial pressure (43±7vs57±9 mmHg, P<0.05) and cardiac index (1.7±0.2vs2.6±0.5 L/min/m², P<0.05), and higher levels of plasma lactate (7.2±2.4vs3.7±1.4 mmol/L, P<0.05), base excess (-6.8±3.3vs-2.3±2.8 mmol/L, P<0.05) and potassium (5.3±0.6vs4.2±0.3 mmol/L, P<0.05) at 30 minutes after hemorrhagic shock compared with surviving animals.</p><p>Conclusions</p><p>The HRV increased early during hemorrhage but none of the evaluated HRV metrics was able to discriminate survivors from non-survivors during hemorrhagic shock. Moreover, metabolic and hemodynamic variables were more reliable to reflect hemorrhagic shock severity than HRV metrics.</p></div

Hemodynamic variables in pigs submitted to acute hemorrhagic shock and fluid resuscitation.

<p>S = survivor group. NS = non-survivor group; * = P<0.05 different from baseline; # = p<0.05 NS group different from the S group (t test).</p

Experimental protocol.

<p>Baseline: before hemorrhage; Hemorrhage15: at the end of blood withdrawal; Shock30: 30 minutes after the end of blood withdrawal; Shock60: 60 minutes after the end of blood withdrawal; R0: at the end of fluid resuscitation; R60: 60 minutes after the end of resuscitation; R120: 120 minutes after the end of resuscitation; R180: 180 minutes after the end of resuscitation.</p

HRV frequency-domain metrics during acute hemorrhagic shock and fluid resuscitation.

<p>VLF = spectral power at the very low frequency; LF = spectral power at the low frequency; HF = spectral power at the high frequency; LF/HF = low to high frequency index ratio; Hemo5 = 5 minutes hemorrhage; Hemo10 = 10 minutes hemorrhage; Hemo15 = 15 minutes hemorrhage; Shock30 = 30 min after hemorrhagic shock; Shock60 = 60 min after hemorrhagic shock; R0 = immediately after fluid resuscitation; R60 = 60 min after fluid resuscitation; R120 = 120 min after fluid resuscitation; R180 = 180 min after fluid resuscitation</p><p>* = P<0.05 different from Baseline</p><p>†<0,05 different from CH5 and CH10</p><p>§ <0,05 different from CH5, CH10 e CH15</p><p>A = P<0.05 group NS different from group S.</p><p>Mean ± SD.</p

HRV time domain metrics in pigs submitted to acute hemorrhagic shock and fluid resuscitation.

<p>S = survivor group. NS = non-survivor group; * = P<0.05 different from baseline; # = p<0.05 NS group different from the S group (t test).</p